#include <stdio.h>
#include <stdlib.h>
#include <math.h>
double AB(double x1,double x2,double y1,double y2);
int main()
{
    double x1,x2,y1,y2;
    while(scanf("%lf %lf %lf %lf",&x1,&y1,&x2,&y2)!=EOF)
    {
      printf("%.2lf\n",AB(x1,y1,x2,y2));
    }
    return 0;
}
double AB(double x1,double y1,double x2,double y2)
{
	double p1,p2;
	p1=pow(x1-x2,2)+pow(y1-y2,2);
	p2=pow(p1,1.0/2);
	return p2;
}